T cells secreting Type 2 cytokines are responsible for much of the pathology associated with asthma. As such, knowledge of the mechanisms that control Th2 generation is important for developing effective therapeutic strategies. We, and others, have suggested that both the differentiation of naive T cells into Th2 phenotypes and the immediate secretion of Th2 cytokines are determined by the quantity and/or quality of signals that are delivered to a T cell either through recognition of peptide/major histocompatibility complex (MHC) or by ligation of costimulatory receptors. This may be the principle of allergen immunotherapy, and studies of human and murine asthma have shown that disease can be manipulated by varying treatments with antigen. The molecular basis for how intracellular signals control Th1 and Th2 responses is largely unknown. In this application, we propose to investigate some of the intracellular signaling molecules and pathways that are integral to promoting Th2 as opposed to Th1 cells and whether these represent feasible targets for suppressing asthmatic reactions. Naive CD4 cells from T cell receptor (TCR) transgenic mice will be assessed for ability to directly produce Th1 and Th2 cytokines and to differentiate into Th1 and Th2 cells. Pharmacological inhibitors and retroviral transduction with dominant negative genes will target various signaling molecules to determine if Th2 responses can be selectively inhibited. Similarly, several novel members of the TNFR family that are expressed on T cells will be targeted to specifically inhibit Th2 cytokines, namely OX40, 4-1BB, and LIGHT. These basic studies will be extended to a mouse model of asthma to investigate therapeutic efficacy in an in vivo setting. Pharmacological and costimulatory inhibitors will be used alone, given either at the time of priming, or at the time of sensitization with aerosolized antigen. These will be combined with therapy using a strong agonist peptide antigen that has been shown to suppress asthmatic symptoms. Our studies may provide valuable information regarding which molecular pathways control Th2 cells and whether targeting these pathways can be of therapeutic benefit to suppress the asthmatic reaction. This project will contribute to the overall goal of the Program by advancing our knowledge of how the Th2 response that dominates asthma is brought about and may lead to the development of new methods for treating and preventing asthma and allergic diseases.